The present invention relates generally to releasable connectors. More particularly, the present invention relates to a releasable connector for a guy wire system. In addition, the present invention relates to a system for releasing a guy wire from an anchor device in the event of a collision.
The United States has between eighty million and one hundred million wooden utility poles along approximately four million miles of public roads. Approximately fifteen hundred to two thousand fatalities and about one hundred thousand injuries occur each year as a result of automotive collisions with utility poles. In an automobile crash with a utility pole guy wire, the car may roll over or it may be thrown into oncoming traffic with disastrous consequences.
Known techniques for reducing the number and/or severity of collisions include: providing lateral separation from the road; placing utility lines underground; shielding poles with guard rails; and providing advanced warning signs, wider shoulders, better lighting, skid resistant pavement, and better roadway alignment. The known techniques are generally too costly and/or too inconvenient for wide-scale implementation, however. Another approach has been to construct the poles in such a way as to reduce the likelihood of injury in the event of a collision. The Federal Highway Administration, for example, has developed a slip base upgrade for utility poles which reduces the likelihood of severe injury in an accident. The problems caused by guy wires, however, have not been satisfactorily resolved in the prior art.
A frangible guy wire device was referred to in xe2x80x9cSafer Timber Utility Poles,xe2x80x9d Volume I, Summary Report, Texas Transportation Institute (xe2x80x9cTTIxe2x80x9d) (September 1986). The device tested by TTI consisted of a six foot length of three-quarters inch galvanized steel pipe. The device relied on stress concentration as the failure mechanism. The stress concentration was formed by a rigid section connecting two pipes. Failure occurs at the pipe threads adjacent to the rigid section. There are several problems associated with the device referred to in the TTI report. One such problem is that stress concentration is not a reliable release mechanism in a guy wire system. It is difficult to control the critical dimensions at the stress concentration point, and corrosion affects the performance characteristics of the device. In addition, the device tested by TTI was unduly sensitive to the bumper height of the colliding vehicle. In particular, the device might fail to release when a car approached from xe2x80x9cunderneathxe2x80x9d the guy wire. In addition, the long pipe itself could create a hazard during a collision, and the device could not be easily rebuilt afterward.
Another known device for a guy wire system is described in U.S. Pat. No. 5,529,276 (Szablya). The Szablya device relies on stress concentration and shock bending stress. As such, it is not sufficiently reliable. The release characteristics of the Szablya device would be dependent on parameters such as surface finish, corrosion, wear and manufacturing tolerances, which may be difficult to control. In general, corrosion is a problem with any outdoor system that relies on stress concentration as a release mechanism. In addition, the parts of the Szablya device that remain with the guy wire after a break could become dangerous moving objects, since they are not tied to the ground. In addition, the Szablya device would be difficult to manufacture, and it would be difficult to rebuild the device after a collision.
The disadvantages of the prior art are overcome to a great extent by the present invention. The present invention relates to a releasable connector device for providing a separation mechanism in a collision. The device may be formed of at least two elongated rigid elements and a tension member located between the rigid elements. During a side impact collision, the rigid elements pivot to amplify the axial stress applied to the tension member, such that the tension member breaks to provide the desired separation. If desired, a flexible connector or tether may be used to prevent the upper rigid element from separating from the lower element.
In a preferred embodiment of the invention, the rigid elements are steel pipes, and the tension element is a threaded steel rod located within the pipes. The present invention should not be limited, however, to the preferred embodiments shown and described in detail herein.
According to one aspect of the invention, a threaded unit is used to hold the upper pipe to the tension member. The threaded unit may be located within the upper pipe, if desired. The threaded unit may be arranged to slide out of the upper pipe along with the threaded rod during a collision.
According to another aspect of the invention, a threaded fixture is located within the lower pipe for connecting the tension member to the lower pipe.
The present invention also relates to a release system that has a connector device interposed between a guy wire and an anchor device. The connector device may be formed of elongated rigid elements in contact with each other at a break point (or at a separation plane). A flexible element may be used to secure the rigid elements together during a collision. The flexible element, which may be a cable, chain or the like, may be used to tie or tether the upper portion of the connector device to the lower portion of the device, to prevent the upper portion from causing damage and/or injury to the vehicle and/or its occupants.
In a preferred embodiment of the invention, a threaded rod is used as the breakable element in the connector device. When a bending stress is applied to the device, for example during a side impact collision, the threaded rod breaks in tension at a preselected break point. The tension in the guy wire causes the broken portion of the rod to be pulled out of the connector with sufficient force to minimize the possibility that the rod will come into contact with the moving vehicle or its occupants.
According to yet another aspect of the invention, the rigid elements are placed in an end to end relationship and a fulcrum bending point is formed between the rigid elements. During a collision, the device bends or pivots at the fulcrum point. The rigid elements themselves do not bend to the extent that any permanent deformation occurs. As a result, the pipe elements may be used in a rebuilt device, after the collision.
The present invention also relates to a method of operating a guy wire system, particularly during a vehicle collision. In operation, the impact force of the vehicle and tensile force in the guy wire create a bending moment in a connector device. The connector device may be interposed between the guy wire and an anchor device at approximately the height of the oncoming vehicle (i.e., the height of the bumper or other impact point of the vehicle). The bending moment causes a breakable element to break in tension. The tensile strength of the breakable element may be greater than that of the guy wire, if desired. The breakable element is broken because of the mechanical advantage applied by placing the connector device in bending.
As the vehicle (a car, truck, etc.) moves through the original location of the connector device, the guy wire tension causes at least a portion of the breakable element to be pulled through an upper pipe. A flexible connection keeps the upper pipe tied to a lower pipe, to reduce the amount of damage that might otherwise be done by the upper pipe. The tension of the guy wire causes the breakable rod to be cast up and over the moving vehicle. The remainder of the connector device remains anchored to the ground, where the vehicle can run over it.
An object of the invention is to provide a device that fails or releases reliably when subjected to a side force above a design threshold.
Another object of the invention is to provide a system that is actuated by automobiles, trucks and other vehicles, and that operates as intended over a wide range of vehicle speeds.
Another object of the invention is to provide a device that releases upon impact regardless of the direction of travel of the errant vehicle.
Yet another object of the invention is to provide a device that can be used in a wide variety of different size guy wire systems and in a variety of environmental conditions.
Another object of the invention is to provide a connector device that reliably performs a breakaway operation in bending at lateral loads smaller than those that would tend to tip a car over or allow it to ride up a guy wire.
Yet another object of the invention is to provide a low cost connector device that can be easily installed and repaired by utility crews.
In a preferred embodiment of the invention, the connector device resembles a slender rod, several feet long. The device is connected in series with the utility pole guy wire. The lower end of the device is hinged to the ground anchor. The upper end of the device is securely attached to the taught guy wire. When struck by an errant vehicle, the device is pushed out of line with the anchor and utility pole attachment points. The tension in the guy wire increases. A component of the tensile force is applied at a right angle to the axis of the device. The transverse force component creates bending moments which operate to break the device in bending, such that the guy wire is released. The tension in the guy wire causes it to snap away from the vehicle to avoid further damage to the vehicle or its occupants. Following an impact event, a utility crew only needs to replace the failed link to place the guy wire back in service. In a preferred embodiment of the invention, the guy wire system may be rebuilt or repaired with hand tools.
The present invention is superior to prior art designs based on stress concentrations at threads, notches or scored areas. Stress concentration devices are highly dependent on device geometry, surface finish and corrosion. Consequently, stress concentration is an unreliable failure mechanism for use in roadside environments.
Another object of the invention is to provide a failure mechanism that functions only in the event of a side impact. In a preferred embodiment of the invention, failure is caused by mechanical amplification of tensile force on a preloaded rod. The mechanical amplification is a function of component geometry specifically, the device diameter, and overall length. The side impact release mechanism and the ultimate tensile strength of the system are mechanically decoupled, and they can be separately engineered.
In a preferred embodiment of the invention, the releasable device has a higher axial tensile strength than the strongest guy wire in common use, yet the device fails reliably in a side impact with the lightest vehicle under consideration, and is not released by an impact from a slowly moving bicycle or by vandalism. Breakaway devices that rely on weaknesses caused by stress concentration, in contrast, can be separated by tension loading and by side impact loading, and therefore require a separate design for every guy wire strength.
These and other advantages and features of the invention will become apparent from the following detailed description which is provided in conjunction with the accompanying drawings.